Maybe they'd accept "I give you a 20% (lifetime) referral fee for the next 10 customers, if you referred them to me or not". That's 20% of revenue but it has a limit and still gives them motivation to either active or passive help you grow. Active could be they send you potential customers, passive could be they give you a great testimonial for your website. They wouldn't own part of your company and structuring such a contract should be straight forward compared to company shares.
